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FEV Advances With Variable Compression Ratio Gas Engine

The variable compression ratio engine uses flex-fuel operation, along with turbocharging and direct injection, to counter the fuel economy drawbacks of E85.

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DETROIT – As a means to exemplify the gasoline engine’s relevance in the face of advancements in alternative powertrains, FEV Engine Technology Inc. continues to develop a variable compression ratio (VCR) system for use with turbocharging and direct gasoline injection.

Showcased at last week’s 2007 SAE International World Congress here, the turbocharged 4-cyl. development engine boasts V-6 power with 4-cyl. fuel economy due to its ability to mesh VCR technology with flexible-fuel operation, FEV says.

“This engine is a look at the future evolution of spark ignition as manufacturers seek to set a new standard for both power and fuel efficiency, yet face increasingly stiffer emissions requirements,” Robert Last, vice president-operations and communications, says, adding FEV expects the VCR engine to achieve diesel-like efficiency when running on E85 (an 85% ethanol/15% gasoline mix).

Utilizing a position sensor and an eccentric gear drive attached to the crankshaft, the VCR system operates by actuating an electric motor to move the centerline of the crankshaft up or down about 0.2 in. (5 mm). This slight movement allows the compression ratio between the pistons and cylinder head to be varied from 8:1-16:1.

Unique couplings at both ends of the crankshaft eliminate torque loss at the engine’s output shaft.

This ability to change the engine’s internal operating parameters translates into fuel economy gains of up to 25% when running on E85, Last says, noting the system can be tuned to provide greater power output, as well.

Because E85 has a much higher octane rating than gasoline (100 octane or more), the engine’s compression ratio can be spiked considerably under full-load without worry of premature combustion, or “piston knock.”

Conversely, compression can be lowered under light-load situations, putting less stress on the engine and allowing it to operate more efficiently.

In the real world, this dynamic ability overcomes the lower energy density of E85 and other alternative fuels, which tend to offer lower fuel economy averages than gasoline, Last says.

The integrated sensors and controls for determining the alcohol content of the fuel, along with the fuel injection and turbocharging systems, all are existing technologies, he adds.

Although FEV won’t be ready to present its findings to customers until sometime next year, Henning Kleeberg, senior engineer-spark-ignited engine development, says the VCR engine will cost more than a conventional gas engine but less than a diesel, with the lower cost of downsizing the engine offsetting the difference.

“It is not a war (between gas and diesel engines),” Last says. “They both are complementary toward reaching the same goal.”

And if that goal involves alternative fuels, they will have to be made from biomass that does not have another purpose, he says of the current issue of increased corn-based ethanol production driving up prices of corn and potentially contributing to food shortages.

“The key to our (energy) sustainability is the conservation of existing fuels,” Last says.

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